I wonder about this all the time.

I think it's possible to have a cultural disorder called depression, because someone had to define it. Other cultures may not recognize the same suite as a related set of symptoms comprising a disorder that can be called depression.

I wonder all the time if certain things I experience should just be chalked up to the normal human experience, not looked at as "pathological." Some of these dark feelings might spur me to greater insights in my life. Sometimes they may even result in great actions later.

It all depends on how you "measure" your life. I'm big on nitpicking my productivity. "Depression" is one of those things that squashes productivity, however one measures productivity. Thus, I identify things that get in the way of the things I want to produce as "bad" and/or "not normal."